I would say Trafalgar was the most decisive. It put an end to Napoleon's plans to invade England or Ireland, which would have had some very serious consequences for the entire world. Most of the others you mention were great historic contests of naval power, but they did not change the world at that instant all by themselves.

> Number of warships involved: About 600 galleys and smaller ships.
> Number of men involved: More than a hundred thousand.
> Number of warships lost: About 30 galleys sunk (15 Christians and 15 Turkish). 190 Turkish galleys captured later.
> Number of men lost: About 38,000 dead (30,000 Turks and 8,000 Christians).
> Consequences and importance of the battle result: Turk expansion stopped and the Western world saved.

I'm in favour of the spanish 'armada' versus the QE fleet (1588 or circa, I don't remember now). Not only because number of ships, amount of losses and men involved, but for the consequences. Best for England, to be free of catholicism till now. Worst for Spain, to suffer catholicism till now. As many other I suspect that God doesn't exist, by if He exist definetely he is english!

I vote for Lepanto - the giant clash of the Cross v. Crescent many ships were destroyed and many thousand were dead.
I wish to add more battles 4 day battle between Dutch and British fleets more than 7000 dead, 21 ships detoyed and captured, Chesma 1770 between Tukish ships and Russian 7000 Turks died and 10 Rrussians
The battle in Vigo bay 7000 Spaniards died in 1704

I think Jutland is the greatest CONVENTIONAL (ie: no aircraft carriers) naval battle of all times. This puts Midway and Leyte Gulf out of the discussion.
Think of it: almost 60 battleships and battlecruisers fighting in the North Sea, two British battlecruisers lost with 3000 lives in a matter of minutes.
For comparision, the Kriegsmarine only have 4 battleships in WWII.
I believe that if the losses were no greater was because of the German decision of not fully engaging with the British fleet.
I think, with my limited knowledge of naval history, that there is no other battle in history in which so much firepower was called upon.

I put Jutland as the biggest, but it was not a decisive battle; infact the Hochseeflotte after Jutland remained in her port, while the naval power of the Grand Fleet was unthouched.

I agree the most decisive battle ever fought has been Trafalgar.And a revolutionary tactic too, when Nelson decided to abandon old line-to-line battle scheme and, as he loved to say, he "headed towards the enemy".
That unespected step and the superiority or british crews and gunnery gave them....the Victory.

Jutland. Even if no one had a full victory the consequences were such that, in the end, favored Britain and led Germany to it´s defeat. (WWI was a defeat in that meaning?).
Well, considering it maybe Lepanto, Trafalgar and Midway had the same efect over History and Society.

It was probably the closest to altering history radically. And more was at stake than the others--in my opinion.

I have read differing opinions of Lepanto--certainly decisive, but I believe the Turks did rebuild their forces rapidly afterwards. Though of course they might have been so intimidated they never tried so hard again to do what they were trying to do at Lepanto.

Trafalgar was decisive of course, but the French and Spanish were so inferior in the crew and leadership quality as to make an alternative victory over the British navy unlikely, and a successful invasion even more so.

Tsushima was pretty close as well. Certainly the Russians never tried to become a serious naval power after that--until after WW II, that is.

Midway certainly turned the war in the Pacific around, but the Japanese never really stood a chance to win it anyway.

Jutland, in terms of massed firepower, yes--and if the Germans had done substantial damage it could have had disastrous consequences. But that would have been difficult to pull off.

A far more dangerous situation for the British was during one of the raids on the coast--when a substantial but not nearly powerful enough segment of the British fleet came close to being overwhelmed by the Germans. But that's a what-if scenario. Furthermore I believe the Germans came close to having their battlecruisers similarly overwhelmed in the same raid. There were two very close calls, for each side respectively. Sorry to digress, though...